Generally, a communications link is be considered to be a communications channel between two or more communicating devices. The communications link utilizes a single carrier frequency or multiple carrier frequencies. Furthermore, a single communications device receives a transmission or multiple transmissions over multiple communications links. The transmission or the multiple transmissions over the multiple communications link can be from a single communications device or from multiple communications devices.
As an example, in a Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) compliant communications system, multiple communications links (commonly referred to as component carriers) can be aggregated to facilitate high bandwidth transmissions between two communications devices.
As an additional example, Multiple Input and Multiple Output (MIMO) technology uses multiple antennas at both communications devices to improve communications performance. MIMO offers increased data throughput and range, often without additional bandwidth or transmit power. MIMO achieves improved performance through higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity. Transmissions between the transmit antennas of a transmitting communications device and the receive antennas of a receiving communications device may comprises multiple transmission layers. Each transmission layer is associated with a set of precoding weights, which is applied to one of the transmit antenna ports.
A precoder is considered to then be a set of precoding weights, with one precoding weight for each transmission antenna and each transmission layer. A MIMO transmission layer is also commonly known as a MIMO stream. The multiple layers of MIMO transmission may be divided into one or more codewords where each codeword may be mapped to one or more transmission layers. Each codeword comprises one or more data code blocks (CB) which are collectively referred to as a transport block (TB). All the transmission layers associated with a codeword are of the same modulation and coding scheme (MCS) while transmission layers associated with different codewords may have different MCS levels. The MCS levels of the codewords may be independently determined at the eNB and signaled to the UE. Each of the MIMO transmission layers or codewords may be considered as a communication link between the two communication devices.
As another example, in Multiple Point transmission, a communications device may receive transmissions from two or more transmission points with each transmission occurring over one or more communications links. As yet another example, in Coordinated Multiple Point transmission, a communications device may simultaneously receive transmissions from two or more transmission points with each transmission occurring over one or more communications links. As a further example, in a heterogeneous communications system, a communications device may receive transmissions from two or more transmission points with the transmission points accessing the heterogeneous communications system using different radio access technologies, potentially different from a radio access technology used by the communications device.